I am researching very nice (very readable and enjoyable) screen fonts for reading ebooks, either in HTML or EPUB format. I want this both as an avid reader and as an ebook formatter. I think the key fonts to choose are those for body text, since that is what one spends almost all one's time looking at. The following is a (long) summary of my search so far.

Criteria for all fonts: Fonts must be free (no charge), and must have a license that allows use, distribution and modification. I'd like to be able to share the books I format with anyone.

Criteria for sans serif text fonts: Fonts should display decently at 6-8 pts, have R/I/B/BI (regular, italics, bold, bold italics), small caps, lining and text figures, and basic Latin ligatures. I say 6-8 pts not because I intend to read long passages at such small sizes, but because I think legibility at small sizes is a very good, and easy to evaluate, indicator of quality at larger text sizes (9-14 pts). A font that struggles at 8 pt doesn't magically turn great at 10 pt.

Judged suitable as a screen body text font: Dejavu Sans, Liberation Sans, PT Sans, and Dejavu Sans Condensed. (I used Microsoft Verdana, Segoe UI, Arial, Corbel, and Calibri for comparison. No wonder people think Verdana is highly readable – the lower case and numerals are huge in comparison to all the others!)

I judged not as suitable as those above: Aller, Aurulent Sans, Candela, CartoGothic, FreeSans, Iwona, Kurier, Linux Biolinum, TexGyreAdventor, TexGyreHeros. All these do have bold/italic variants.

Fairly suitable, but judged superfluous in the end: Arimo, Lato, and Nobile. Lato is worth revisiting later in 2011 if/when the character set is expanded. Droid Sans would be listed here too, but it has no italic.

I have yet to find a suitable typewriter font. "Courier New" and “Courier” covers Windows and Mac for now, but not Linux and e-book readers.

Other fonts (e.g. men's and women's handwriting for letters, notes, decorative, etc.): These vary in style greatly, and many are available at free font sites (e.g. FontSquirrel, Google Fonts). Select as each particular book, passage or character suggests. No general need for font variants or features.

At this point, the Dejavu fonts were my favorite.

Having found three serif, three sans serif, and two monospaced fonts that met the first requirement, I compared the color and spacing of each on a sample screen page consisting of two identical paragraphs of “lorem ipsum” text (courtesy of www.lipsum.com), each marked up in one font. Using text you don't understand lets you concentrate on the appearance rather than the meaning. Here is the sample paragraph, in case someone wants to try this themselves:

I compared the relative appearance of the text in each font, highlighting any character spacing or other appearance or readability issues as I went so I could review and count them. I ran the test at two point sizes for each comparison to make sure the results were valid.

During the exercise, it became obvious that the Dejavu fonts are not as well spaced as the other two. Counting the highlights, I averaged between 30-40 marks per the above paragraph in point sizes 10-12 for both the serif and sans regular Dejavu fonts. I averaged less than 10 marks for each of the other two – Liberation and PT (Paratype). This overrode any other differences. To my eye, the Dejavu font spacing issues (on my system, who knows what they look like on another) are quite an unpleasant distraction from reading. Spacing is not a barrier to reading pleasure with either of the other two font families.

Comparing Liberation v PT fonts required consideration of other things besides spacing, and being more specific. In the regular sans, the two fonts are approximately the same size. Liberation Sans would benefit from the greater line spacing of PT Sans. The PT Sans “M” is a bit dark in color on the screen, and catches the eye a bit (this seems to be a common problem). Also, strangely, I noticed the PT Sans space character is too narrow for my comfort. I have never noticed this in a font before. Either of these two fonts could be very acceptable for long sessions of reading.

On the serif side, PT Serif is noticeably larger than Liberation Serif. PT @ 10pt is about the same visual size as Liberation at 11.5pt. Unlike the sans fonts, the interline spacing is similar. There are no problems with the PT “M” or space character. PT may have slightly better spacing than Liberation in general - it just looks smoother.

The big difference between these two serif fonts is the glyph shapes. PT Serif has rounder glyphs; Liberation Serif is squarer, and adds an overall impression of emphasis on vertical strokes that may not be as appealing for some. The only functional issue is with the Liberation lower case “m”. Its squareness across the top makes it too hard to distinguish from “rn”. I would enjoy long reading sessions with PT Serif, but not as much so with Liberation Serif.

That's where I am now. I think neither PT nor Liberation has text figures or small caps. I may be able to hack tolerable small caps in CSS. There's nothing to be done about the text figures, though, unless I copy them from another font.

BTW, all these fonts have extensive character sets, and the files are quite large compared to most Western font files. If you want to use them, you should either install them on your reading device, or "subset" them - remove the parts you don't need - before embedding them in an EPUB book or an HTML package or WOFFing them. Is WOFF a verb yet?

As of 8 March 2011, the current version of Dejavu font package is 2.33, the Liberation font package is 1.06, and the PT font version is 2.003 (from Sans font file).

We press on. I didn't mention that I am using two apps to look at the fonts: Firefox 4 and LibreOffice Writer. That way I avoid unusual things due to just one type handling system (I hope). Later, I want to see the final selections in another browser, and on an e-ink device (nook).

I wanted to get Dejavu back in the running if I could, reconsider Droid Serif, and throw in a new contestant: Arvo, the first slab serif to be examined.

Remember Dejavu had a letter spacing problem (or Win7 had one with the font). To try to rehabilitate Dejavu, I ran the regular sans and serif fonts through the @fontface generator at FontSquirrel (http://www.fontsquirrel.com/fontface/generator) to see what would happen. It includes an auto-hinting option for better display in Windows, so I used that option to try to solve my issue.

I installed the new versions of Dejavu and the downloaded Arvo and Droid Serif. I didn't think such a simple thing as auto-hinting would work on the Dejavu fonts, but it did! Both the sans and serif fonts displayed none of the issues I saw earlier. I haven't confirmed that the other variants (italic, bold, etc) of Dejavu will be improved for Windows use by autohinting, but I am very encouraged.

Both Arvo and Droid Serif are legible at 6 pt (Arvo less so than the others), and have no significant problems with my simple color and spacing test paragraphs. Arvo looks light at these small sizes - it may be more intended as a display font.

The FontSquirrel @fontface generator also lets you subset the font's character set, so I can reduce font file size drastically (by 5x or more) by picking the Unicode ranges or languages I want to keep. So that problem is also solved.

Eight body text choices, five serif and three sans, are more than enough. For setting sans and serif fonts in the same book, it is nice to have pairs that work well together. It's clear that both the Droid and PT families were designed to do just that; that leaves the Liberation and Dejavu families and Arvo to check. I used a small book chapter, again in html and LibreOffice, to do the compatibility tests.

As expected, Droid Sans and Serif, and PT Sans and Serif, look great together. I have much more mixed feelings about both Liberation and Dejavu. Liberation is a metric-compatible substitution for Times New Roman and Arial, and I was not fond of using those two together over twenty years ago, and I'm still not today. The two families have the same general problem: the sans and the serif fonts don't match, and they also aren't distinctly, consistently different. There is some confusion at the individual glyph level. So I'm not sure what to do there.

PT Sans and Arvo don't look too bad together. But I'm not convinced Arvo is up to the task on its own. Looking at more samples will help, and maybe running it through FontSquirrel. I'dl ike to have a good slab serif as a option.

With the help of Fontforge, and spelunking in Constantia, I have come a long way in adding small caps, numeric subscripts, numeric and lower case superscripts, numerators and denominators, and text ("old style") figures to the two regular Dejavu fonts. Fontforge does everything but the old style figures automagically.

The text figures take more manual work. But it is pretty simple: copy the standard monospaced titling figures to a new location in the font and rename them ("nine.oldstyle"). Then there is a tradition for what to do with each digit. The 6 and 8 remain unchanged. The 0, 1, and 2 get squished down to the height of the lower case letters. The 3, 4, 5, 7, and 9 get dropped down (not squished) to match the height of the lower case - their bottoms hang below the baseline. Last, reset the widths so the numbers are proportional width, not monospace (the "1" gets the biggest change). Set up an Opentype table tagged "onum" to point to them, and, in theory, you are done.

So I'm pretty sure I can meet my requirements with at least three families: Droid, PT, and Dejavu. I'm not sure Liberation adds anything extra to those three, so it's optional. And I'd like to keep Arvo, or another slab around.

Since most ePubs don't require anything larger than 16pt, or at most 20pt, I see little reason to spend much time on display fonts. They barely begin to show their character at those sizes.

Does anyone have any advice, suggestions, or requests while I am going about tailoring these fonts for e-books?

I like a font with a large ascender height. I think that makes the paragraph more readable without having to change the line height manually.

The ascender height is not necessarily related to the leading (line height). The leading depends ultimately on the size of the box inside which the characters (glyphs) are drawn. The ascenders and descenders may fit in this box, may leave some unused space above and below, or may extend outside this box.

I was most interested to find this thread. Have you completed producint the fonts? If so I would be interested in seeing and perhaps using them.

How many words does each font give you?

No, I haven't completed them in the sense I would post them somewhere. I got them to a point where I enjoyed using them, to varying degrees, and have let it lapse for a couple months.

There is so much difference in size between fonts that are nominally the same size, e.g. 10 points, that giving the number of letters per line at a point size doesn't have much meaning. Also, some fonts are fat and short, and some tall and skinny. I find for comfortable reading, I need more than the minimal amount of spacing needed for letter recognition. This is probably something that varies with each individual. What one should consider is the total amount of text that can be presented on a page/screen using that text font.

I did some research into legibility and readability of typefaces, and the biggest differences by far have nothing to do with letter shape or proportion or weight or serif/sans. The two main factors are: 1) a larger letter is always easier to read, and read quickly and comfortably, than a smaller one,and 2) familiarity - if a person is used to seeing a style of print, they read it better than new styles - even if the familiar one is much inferior to the new one.

I'd like to see some pictures, of the fonts, on their own and side-by-side.

I like a font with a large ascender height. I think that makes the paragraph more readable without having to change the line height manually.

Pictures of them as displayed on what screen?

Fonts with large ascender heights are old-school now. Commercial fonts for text tend to maximize the height of the lower case to improve readability while keeping the text blocks compact.

From the research I did, I came to the conclusion that it is likely that descenders are a hindrance to reading, because they interfere with a quick smooth return of the eye to the beginning of the next line. I tested this by making a font that replaced all the lower case letters with small caps. For me, at least, it works very well. I'm sure there are better ways to test it, though.

No, I haven't completed them in the sense I would post them somewhere. I got them to a point where I enjoyed using them, to varying degrees, and have let it lapse for a couple months.

I am sorry to hear that you have not completed the fonts to the point where you would be happy to post them but look forward to seeing them when you are ready to do so. I hope to do similar projects myself when I retire in a couple of years and hopefully will have the time (my wife has plans!).